The formation of a 26m ice cover on Lake Vida, Antarctica

Lake Vida, the largest lake in the McMurdo Dry Valleys of Antarctica, has the thickest ice cover of any lake on Earth. In order to understand the controls on lake formation, and the antiquity of the ecosystem, 40 ground penetrating radar transects and two ice cores (21 and 26.5 m deep) were obtained in the fall of 2010. The ice cores are characterized by three distinct facies. With depth, the ice transitions from cold dry lake ice, to brine saturated ice at 16 m, and then to sediment-laden ice interbedded with sediment layers (up to 25 cm thick) below 21 m. The crystallography of the basal ice, which is at least 3000 years old, is not characteristic of lake ice, but instead resembles glacial ice that has undergone strain. Furthermore, the upper layers act as an aquiclude to highly saline (188 ppt) and pressurized brine which is trapped below 16 m. We hypothesize two scenarios for the formation of this basal sequence. Firstly, ancient glacial or lake ice may have been buried by repeated fluvial or aeolian deposits. The alternative option is that the ice is segregation ice formed in situ within sediments that were already deposited. The pressure head, which may be compensated by a partially floating ice cover, may have originated due to a reduction in ice porosity from gradual freezing over time. Elucidating the formation of Lake Vida provides an interpretation of past climatic conditions in the McMurdo Dry Valleys, and places critical constraints on how microbes survive in isolated environments. In addition, the stability of the buried basal ice and the antiquity of the brine provide an analog to assess the last vestige of water on other planets.